Modelling of slab supporting on piles

Question

Hi guys, 
 
 I am modelling a slab supported on piles, the piles are actually tension piles to support upheave beneath the slab. I model the slab using plate elements and use vertical restraint node support at where the piles are located. The issue I am facing here is that, the out-of-plane shear will be very high, especially at those localized area and also closer to the edge of slab. I think that those shear is not realistic. I have read somewhere that, modelling some dummy members might help but I am not sure how to do it or if there is other methods to resolve this issue. There is no beams in the structure, only slab and piles. I have included a few snap shots of the loading conditions and out-of-plane shear results. I am pleased to attach my staad file here too. 1261.Launch chamber.STD

Best regards, 
 Ze Yang Lee

Modestas · Answer

Check a 2nd point in this Wiki: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/29385/avoiding-stress-concentrations As it suggests, you may connect the support node with adjacent nodes by using the dummy members, which would have a material with high E value and low density. This would spread the stresses and reduce it.

Modestas · Answer

Think about the support nodes as a concentrated load on the mat. You do not need to create dummy members around the perimeter. Instead, create a dummy member between the support node and some nodes around that support node.

Sye · Answer

The stress value I see from your plot are 1284 kPA which is only 1.284 N/mm2. When you say high stresses, what stresses are you expecting ? On a side note, the DUMMY material you defined has a very low E value ( should be 1000 times that of the material you used for the other entities). However it may not make much of a difference in your case as I do not see high stress anyway.